Heat treatment apparatus and cleaning method of the same

ABSTRACT

A semiconductor wafer is contained in a reaction tube, and the reaction tube is exhausted through an exhaust pipe while supplying ammonia and dichlorosilane into the reaction tube. A silicon nitride film is deposited on an object to be heat-treated by a reaction of ammonia and dichlorosilane. Subsequently, TEOS is supplied into the reaction tube, while the reaction tube is exhausted through the exhaust pipe. A silicon oxide film is deposited on the object by resolving the TEOS. A semiconductor wafer on which a laminated layer of the silicon nitride film and the silicon oxide film is formed is unloaded from the reaction tube. Then, reactive products attached into the exhaust pipe and the reaction tube are removed, by conducting fluoride hydrogen thereinto, thereby cleaning the pipes. The top end of the exhaust pipe is split into two vents, either one of which is used for discharging exhaust gas for forming films and the other one of which is used for discharging HF gas for cleaning the pipes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat treatment apparatus and acleaning method of the same, and more particularly to a heat treatmentapparatus in which reactive products are prevented from attachingthereinto and a cleaning method of the same.

2. Description of the Related Art

A silicon oxide film (SiO₂ film) or a silicon nitride film (Si₃N₄ film)is used in various sections of a semiconductor device.

An SiO₂ film is produced by resolving alkoxysilane in a decompressionCVD device, etc. An unreacted substance of alkoxysilane[(SiC_(x)H_(y)O_(z))_(n) X=0.1 to 2, y=1 to 15, z=0.1 to 5, n>0]attaches into the CVD device in a process for producing an SiO₂ film.Such a substance comes off in a process for forming a film, and becomesparticles. This process has the drawback of lowering the quality ofto-be-manufactured semiconductor devices and of having a low overallyield.

An Si₃N₄ film is produced by a reaction of, for example, ammonia (NH₃)and dichlorosilane (SiH₂Cl₂) in the CVD device. While a silicon nitridefilmi is being formed, ammonia chloride (NH₄Cl) may be in a state ofsolidity in a low-temperature section of a reaction tube. If the ammoniachloride is sublimated when loading a semiconductor substrate andattaches to the semiconductor substrate, it becomes a source forparticles to be formed on the surface of the substrate in a process forforming a film. Particles which have been formed as a result of areaction of the sublimated ammonia chloride and moisture within theatmosphere attach onto the semiconductor substrate, resulting in adefective feature of the semiconductor device.

The temperature and the exhaust conductance of a manifold of a reactiontube, the periphery of an exhaust section and an exhaust pipe are lowerthan those of a film-forming area where a wafer boat is arranged.Therefore, a lot of reactive products are likely to attach into thosesections.

Accordingly, the conventional heat treatment apparatus has been takenapart in order to clean its composing elements for large scalemaintenance, while the operations of the apparatus are suspended for along period of time. Therefore, only a low operational rate of theapparatus has been achieved.

In order to prevent the apparatus from being operated at a lowoperational rate while cleaning its composing elements, UnexaminedJapanese Patent Application KOKAI Publication No. H5-214339 discloses amethod of cleaning an apparatus forming silicon nitride films with usingHF gas. In addition to this, Unexamined Japanese Patent ApplicationKOKAI Publication No. H4-333570 discloses a method of cleaning anapparatus by removing nitrogen silicon therefrom with using HF gas. Thereferences cited disclose merely a method of cleaning an apparatus byremoving (SiC_(x)H_(y)O_(z)) _(n) with using HF gas and by removingnitrogen silicon. In the references, no disclosure has been made to amethod of forming films in a heat treatment apparatus and a method ofcleaning the same The references do not even disclose a technique forpreventing HF gas used for the cleaning from contaminating theenvironment.

In various processes for manufacturing semiconductor devices, atwo-layered film, such as SiO₂/Si₃N₄, etc. or three-layered film, suchas SiO₂/Si₃N₄/SiO₂, etc. is used. Conventionally, an SiO₂ film and anSi₃N₄ film have been produced in different apparatuses. Thus, whentransferring a wafer from one apparatus to the other, a natural oxidefilm and particles obviously attach onto the surface of the wafer. Thiscauses the problem of lowering the quality of to-be-manufacturedsemiconductor devices and of having a low overall yield.

Accordingly, it is preferred that an apparatus can form the SiO₂ filmtogether with the Si₃N₄ film. However, no proposal has yet been made foran apparatus in which particles are prevented from attaching thereinto.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made in consideration of theabove, in order to clean a heat treatment apparatus with efficiency.

An object of the present invention is to provide a method of efficientlycleaning an apparatus capable of producing various kinds of films.

Another object thereof is to provide a technique for cleaning a heattreatment apparatus with using HF gas while preventing the used HF gasfrom contaminating the environment.

In order to achieve the above objects, according to the first aspect ofthis invention, there is provided a heat treatment apparatus, comprising

a reaction tube which can contain an object to be heat-treated;

an exhaust pipe, one end of which is connected to the reaction tube, forexhausting gas contained in the reaction tube;

a reactant-gas supplying pipe, which is conducted into the reactiontube, for supplying reactant gas into the reaction tube;

an HF-gas supplying section which includes

an HF pipe connected to a gas source for hydrogen fluoride,

an HF valve which controls to supply hydrogen fluoride from the gassource and which is arranged in the HF pipe, and

an inlet which conducts, into the exhaust pipe and/or the reaction tube,the fluoride hydrogen supplied from the gas source through the HF pipe,

wherein the HF valve is open and the fluoride hydrogen gas is conductedfrom the gas source into the exhaust pipe and/or the reaction tube,thereby cleaning inside of the exhaust pipe and/or the reaction tube.

In the structure, an inlet for supplying HF gas is arranged in thereaction tube separately from the reactant-gas supplying pipe. When anHF valve is open, HF gas can be conducted into the reaction tube and/orthe exhaust pipe which can then be cleaned. Therefore, the heattreatment apparatus can be cleaned with simple treatments only.

In the structure disclosed in Unexamined Japanese Patent ApplicationKOKAI Publication No. H5-214339, as shown in FIG. 2 included in thePublication, HF gas and reactant gas are conducted into a reaction tubefrom an identical gas-supplying section. Therefore, the reactant gas isfearfully contaminated in a process for forming a film.

Unexamined Japanese Patent Application KOKAI Publication No. H4-333570suggests (1) a method for conducting HF gas into an apparatus which canform thin films and (2) a method for conducting HF gas into a cleaningapparatus by inserting the apparatus itself into the cleaning apparatus.However, no disclosure has been made to a “structure for efficientlyconducting HF gas into the apparatus so as to clean the apparatus”.

The other end of the exhaust pipe may be split into a first and secondvents; and

a valve may be arranged between the first and second vents, may conductexhaust gas into the second vent when HF gas is exhausted, and conductexhaust gas into the first vent when no HF gas is exhausted.

According to this structure, the products produced while forming a filmand the HF gas used for cleaning the apparatus can separately beheat-treated. An HF gas scrubber may be used as the second vent, whereasa scrubber for any other kind of gas may be used as the first vent.

In the heat treatment apparatus, there may be arranged a plurality oftraps which are arranged on the exhaust pipe and which remove a reactiveproduct within the exhaust pipe, and

a pressure control valve which is arranged between the plurality oftraps and which maintain pressure within the reaction tube and theexhaust pipe at a fixed value.

It is necessary to maintain the pressure within the reaction tube andthe exhaust pipe at an appropriate value in order to form a film andclean any part of the apparatus. The pressure control valve controls thepressure by itself or together with any other device. Since the pressurecontrol valve is arranged between the plurality of traps, the reactiveproducts are prevented from attaching to the pressure control valve(normally, the reactive products easily attach thereto).

The reaction tube includes an inner tube, whose upper end is open, andan outer tube, which surrounds the inner tube with a predetermined spaceand whose upper ends is closed. In this case, it is preferred that theinlet conducts HF gas into the inner tube, and the exhaust pipe isconnected to the outer tube and exhausts gas from the gap between theinner and outer tubes. In having such a structure, the HF gas from theinlet cleans inside of the inner tube toward the upper end of the innertube, and reaches the exhaust pipe through the space between the innertube and the outer tube. Thus, cleaning what is so-called “verticaldouble tubes” can be performed with efficiency.

It is preferred that the inlet is arranged in a position adjacent to anintake (the most upstream side) of the exhaust pipe. Conductance variesin the portion through which exhaust gas passes from the reaction tubeto the exhaust pipe. This results in reactive products easily attachinginto the periphery of the intake of the exhaust pipe. When the inlet isthus arranged in a position adjacent to the intake of the exhaust pipe,the products which have attached into a bent part can be removed withefficiency.

In a case where the exhaust pipe includes at least one bent part, it ispreferred that the inlet is arranged on an upstream side of agas-flowing path and adjacent to the bent part of the exhaust pipe.Conductance of the bent part is low, therefore, a reactive product islikely to attach to the part. If the inlet is arranged adjacent to thebent part on the upstream side of the gas-flowing path, the productswhich have attached to the bent part can be efficiently removed.

In a case where the trap is arranged on the exhaust pipe, the inlet ispreferably arranged adjacent to the trap on the upstream side of thegas-flowing path. Conductance of the trap is also low, therefore, areactive product easily attaches thereto. If the inlet is arrangedadjacent to the trap on the upstream side, the products which haveattached to the trap can be efficiently removed.

The reactant-gas supplying pipe conducts alkoxysilane into the reactiontube in order to form a silicon oxide film on the object, and/orconducts ammonia and a silicon compound (for example, monosilane (SiH₄),dichlorosilane (SiH₂Cl₂), silicon tetrachloride (SiCl4)) into thereaction tube in order to form a silicon nitride film on the object, and

the reaction tube forms a silicon oxide film on the object by resolvingalkoxysilane, and/or forms a silicon nitride film on the object by areaction of ammonia and a silicon compound.

In such a structure, a silicon oxide film and a silicon nitride film cansuccessively be formed in a single one heat treatment apparatus.Furthermore, the products produced in the process for forming thesilicon oxide film and the products produced in the process for formingthe silicon nitride film are efficiently removed with using HF gas.

The exhaust pipe may include an SiO₂ product trap (for example, a disktrap), in the exhaust pipe, which removes a reactive product produced byresolving alkoxysilane within the exhaust pipe,

an SiN product trap (for example, a water trap) which removes a reactiveproduct produced by a reaction of ammonia and a silicon compound withinthe exhaust pipe; and

a heater which heats up the SiO₂ product trap in a range between 100 to150° C.

The pressure control valve is preferably arranged between the SiO₂product trap and the SiN product trap and is heated up by the heater.

The pressure control valve is preferred to maintain the pressure withinthe exhaust pipe at a pressure value of 10 kPa or higher.

The apparatus may further include a heater which heats up the exhaustpipe in a range from 100 to 200° C.

The apparatus may further include a heater which heats up the reactiontube and which heats up the exhaust pipe in a range from 100 to 200° C.

The apparatus may further include a pressure controller which controlspressure of hydrogen fluoride within the exhaust pipe to be fluctuated.The pressure of the hydrogen fluoride within the exhaust pipe isfluctuated, therefore, the hydrogen fluoride spreads over the exhaustpipe even in a part where the conductance is low or in a dead space (apart, such as a cavity, a space between connected portions, etc.,through which gas does not flows), resulting in cleaning the entireapparatus evenly.

The pressure controller controls the pressure within the exhaust pipe tobe fluctuated in a range, for example, 0.1 kPa to 30 kPa. Since thepressure is fluctuated in such a range, the hydrogen fluoride thusspreads over

The pressure controller is preferred to control the pressure within theexhaust pipe to be fluctuated in such a way that a period at which thepressure is 10 kPa or higher and a period at which the pressure is lowerthan 10 kPa are cyclically repeated, and that the period at which thepressure is 10 kPa or higher can be obtained longer than the period atwhich the pressure is less than 10 kPa.

The heat treatment apparatus of this invention may further include apurge-gas supplying section which supplies purge gas into the exhaustpipe and/or the reaction tube; and

a controller which repeats, after the HF-gas supplying section stopssupplying hydrogen fluoride a plurality of cycles of exhausting andsupplying purge gas into the exhaust pipe and/or the reaction tube bythe purge-gas supplying section and the exhaust pipe, and which suppliesfilm-forming gas by the film-forming gas supplying section during theplurality of cycles.

The HF gas is preferred to be purged immediately after cleaning iscompletely performed. In the above structure, the film-forming gas issupplied during the plurality of cycles of exhausting and supplying thepurge gas into the exhaust pipe, thus, the exhaust pipe can be purged ofthe exhaust gas in a short time.

The film-forming gas supplying section supplies alkoxysilane as thefilm-forming gas, while the purge-gas supplying section suppliesnitrogen gas as purge gas.

According to the second aspect of the present invention, there isprovided a method of cleaning at least one of a reaction tube which isincluded in a heat treatment apparatus and an exhaust pipe which isconnected to the reaction tube, the method comprising:

a loading step of loading an object to be heat-treated into the reactiontube;

a first film-forming step of forming a first film on the object, bysupplying first reactant gas into the reaction tube;

a second film-forming step of forming a second film on the object, afterstopping supplying the first reactant gas into the reaction tube andsupplying second reactant gas which differs from the first reactant gas;and

a cleaning step of removing a product produced in the first film-formingstep and a product produced in the second film-forming step which haveattached to at least one of the reaction tube and the exhaust pipe, byexhausting gas contained in the reaction tube through the exhaust pipeand supplying hydrogen fluoride gas into at least one of the reactiontube and the exhaust pipe.

During the cleaning process, it is preferred that the method includes

a raising step of raising temperature of the reaction tube and heatingup the exhaust pipe in a range from 100 to 200° C.; and

a maintaining step of maintaining pressure within the exhaust pipe in arange between 10 kPa to 30 kPa.

The method may comprise a cleaning step of cleaning at least one of thereaction tube and the exhaust pipe by supplying hydrogen fluoride gasthereinto, while controlling the pressure within the exhaust pipe to befluctuated in a range between 0.1 kPa and 30 kPa.

In this case, it is preferred that the method comprises a controllingstep of controlling pressure within the exhaust pipe to be fluctuated insuch a way that a period at which the pressure is 10 kPa or higher and aperiod at which the pressure is less than 10 kPa are cyclicallyrepeated, and that the period at which the pressure is 10 kPa or highercan be obtained longer than the period at which the pressure is lessthan 10 kPa.

The film-forming step includes a step of forming, on an object to beheat-treated, a silicon oxide film by resolving alkoxysilane, and

the second film-forming step includes a step of forming, on the object,a silicon nitride film by a reaction of ammonia and a silicon compound.

In this case, the cleaning step includes a step of exhausting thereaction tube through the exhaust pipe and a step of supplying hydrogenfluoride into at least one of the reaction tube and the exhaust pipe,thereby removing a reactive product which is produced by resolvingalkoxysilane and a reactive product which is produced by a reaction ofammonia and a silicon compound and both of which have attached to atleast one of the reaction tube and the exhaust pipe.

Impurities being exhausted are removed in various positions of theexhaust pipe by a trap, and pressure of hydrogen fluoride gas iscontrolled in a position between the plurality of traps, by controllingan opening degree of a gas-flowing path of the exhaust pipe.

The exhaust pipe is decompressed, after supplying the hydrogen fluoridegas,

film-forming gas is supplied into at least one of the reaction tube andthe exhaust pipe, after repeating supplying purge gas and decompressingthe exhaust pipe for a given number of times, and

supplying purge gas and decompressing the exhaust pipe are repeated fora given number of times again, thereby removing the hydrogen fluoridegas.

In this case, the purge gas is composed of nitrogen gas, etc., while thefilm-forming gas includes alkoxysilane, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

These objects and other objects and advantages of the present inventionwill become more apparent upon reading of the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a diagram showing the structure of a vertical heat treatmentapparatus according to the first embodiment of the present invention;

FIG. 2 is a diagram showing the vertical heat treatment apparatus whichis shown in FIG. 1 and from which a wafer boat for heat treatment isunloaded;

FIG. 3 is a diagram exemplifying a state in which particles contained ina reaction tube are exhausted;

FIG. 4 is a graph illustrating, when cleaning a reaction tube,fluctuations of the pressure within the reaction tube included in avertical heat treatment apparatus according to the second embodiment ofthe present invention;

FIG. 5 is a sequence diagram for explaining operations of a verticalheat treatment apparatus according to the third embodiment of thepresent invention;

FIG. 6 is another sequence diagram for explaining operations of thevertical heat treatment apparatus according to the third embodiment ofthe present invention;

FIG. 7 is a diagram showing a modification of a vertical heat treatmentapparatus;

FIGS. 8A and 8B are diagrams for exemplarily explaining the structure ofan inlet, more specifically, FIG. 8A is a cross section of a manifoldand an exhaust pipe, whereas FIG. 8B is a cross section of an exhaustport;

FIGS. 9 and 10 are diagrams for exemplarily explaining the structure ofan inlet, and each illustrating a cross sectional view of a manifold andan exhaust pipe;

FIGS. 11 and 12 are diagrams for exemplarily explaining the structure ofan inlet, and each illustrating a cross sectional view of an exhaustport; and

FIG. 13 is a diagram showing a modification of a vertical heat treatmentapparatus according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Preferred embodiments of the present invention will now be explainedwith reference to the accompanying drawings.

FIG. 1 illustrates the structure of a vertical heat treatment apparatusaccording to the first embodiment of the present invention.

This vertical heat treatment apparatus is one capable of forming both asilicon nitride film and a silicon dioxide film. The vertical heattreatment apparatus of this invention includes a cylindrical reactiontube (reaction chamber) 11 with long sides held in vertical. Thereaction tube 11 has the double-tube structure having an outer tube 12with an open lower end and an inner tube 13 with an open upper and lowerend. The outer tube 12 is made of a thermal resistance material, such asquartz, etc. The inner tube 13 is formed in a concentric circle insidethe outer tube 12 at an appropriate distance away from the inner wall ofthe outer tube 12.

A wafer boat (boat for heat treatment) 14, made of quartz or the like,is arranged in the reaction tube 11. A plurality of semiconductorsubstrates (semiconductor wafers) 15 as objects to be heat-treated areperpendicularly deposited at predetermined intervals in the water boat14.

A heater 16, which is made of a resistance hearing element, etc., is soformed as to surround the circumference of the reaction tube 11.

A manifold 17 is so arranged under the outer tube 12 as to support theouter and inner tubes 12 and 13. The manifold 17 is made of, forexample, stainless steel, SiO₂, SiC, etc.

A flange 18 is annularly formed in the upper portion of the manifold 17,and is hermetically connected to a flange 19 which is formed in thelower portion of the outer tube 12 via an“O” ring 20 made of elasticmaterials. The lower portion of the inner tube 13 is placed on a support21 which is projected inward from the inner wall of the manifold 17.

First to third gas supplying pipes 31 a, 31 b and 31 c, which are madeof quartz, etc. and are bent toward a heat treatment area (upward), arehermetically seated in one side of the manifold 17 with using a sealagent.

The first gas supplying pipe 31 a is connected to a gas pipe 33 a via ajoint 32 a. The first gas pipe 33 a is connected to a first gas source35 a via a mass flow controller (MFC) adjusting an amount of flowing gasand a valve VB1 controlling the flow of gas. The first gas source 35 ais a gas source for supplying a silicon compound such as dichlorosilane(SiH₂C₂), monosilane (SiH₂), silicon tetrachloride (SiCl₄), etc. Thefirst gas pipe 33 a is connected also to a nitrogen gas source 36 a viaan MFC 34 a and a valve VB3.

The second gas supplying pipe 31 b is connected to a second gas pipe 33b via a joint 32 b. The second gas supplying pipe 33 b is connected to asecond gas source 35 b via an MFC 34 b adjusting an amount of flowinggas and a valve VB2 controlling gas to flow or not to flow. The secondgas source 35 b is a gas source for supplying ammonia (NH₃). The secondgas pipe 33 b is connected also to a nitrogen gas source 36 b via theMEC 34 b and a valve VB4.

The third gas supplying pipe 31 c is connected to a third gas pipe 33 cvia a joint 32 c. The third gas pipe 33 c is connected to a third gassource 35 c via an MFC 34C and a valve VB5. The third gas source 35 c isa gas source for supplying alkoxysilane, preferably tetraethoxysilane(hereinafter referred to merely as TEOS).

A lid (cap) 51 formed in a disk-like shape is hermetically connected toa flange 22 formed in the lower portion of the manifold 17 through an“O” ring 52 made of an elastic material, etc. A heat insulating cylinder53 on which the wafer boat 14 is placed is arranged on the upper surfaceof the lid 51 The lid 51 is attached to an elevator mechanism 54 whichmoves upward and downward in order to load and unload the heatinsulating cylinder 53 and the wafer boat 14 into the reaction tube 11.

An inlet 64 a for conducting hydrogen fluoride (HF) (for cleaning) intothe reaction tube 11 is connected to the lower side of the manifold 17.Further, the inlet 64 a is connected via a fourth gas pipe 33 d and thevalve VB6 to a fourth gas source 35 d as a gas source for supplyinghydrogen fluoride.

The fourth gas source 35 d is connected also to an inlet 64 b via thevalve VB6 and a fifth gas pipe 33 e, and also to an inlet 64 c via thevalve VB6 and a sixth gas pipe 33 f.

An exhaust port 61 is connected to the other side of the manifold 17.The exhaust port 61 is made of stainless steel, etc. and is connectedvia a joint 62 to an exhaust pipe 63 for exhausting exhaust gas.

The exhaust pipe 63 includes pipes 63 a to 63 c. The pipe 63 a isconnected to the exhaust port 61 via the joint 62 so that exhaust gasfrom the reaction tube 11 is conducted into the pipe 63 b. The pipe 63 bis so connected that exhaust gas is conducted from a hot disk trap TRP1into an intake of a vacuum pump VP subsequently via a combination valveCV and a switching trap TRP2. One end of the pipe 63 c is connected tothe intake of the vacuum pump VP, whereas the other end thereof is splitinto two vents 71 and 72.

A factory exhaust pipe 63 d for conducting exhaust gas passing throughthe pipe 63 a out of the pipe 63 d is connected to a predeterminedposition of the pipe 63 a. The factory exhaust pipe 63 is composed of afactory exhaust valve EV, which can be opened and closed, and anon-illustrative damper, etc.

The vertical heat treatment apparatus of this invention includes anexhaust path heater 65 for heating the pipe 63 a and the combinationvalve CV.

The pipe 63 a are bent in some points. The inlet 64 b for conductinghydrogen fluoride into the pipe 63 a is connected onto the upstream sideperipheral to one bent point of the pipe 63 a. The inlet 64 b isconnected to the fourth gas source 35 d via the fifth gas pipe 33 e andthe valve VB6.

An inlet 64 c for conducting hydrogen fluoride into the hot disk trapTRP1 is connected onto the upstream side peripheral to a gas intake ofthe hot disk trap TRP1. The inlet 64 c is connected to the fourth gassource 35 d via the sixth gas pipe 33 f and the valve VB6.

The hot disk trap TRP1 absorbs hydrocarbon C_(x)H_(y) (x and y are bothnatural numbers), etc., produced when producing SiO₂ from TEOS. The hotdisk trap TRP1 includes a housing, a disk assembly, a cover and aheater. A gas intake and a gas exit through which exhaust gas flows inand out are arranged on the both sides of the housing. Contained in thehousing are a disk assembly and a cover in the housing.

The gas intake of the hot disk trap TRP1 is connected to the pipe 63 a,while the gas exit is connected to the combination valve CV via the pipe63 b.

The disk assembly formed in a cylindrical shape are open in its bothends. The disk assembly contains a plurality of disks, made of anadsorbent, etc., which are perpendicularly arranged at predeterminedintervals in a direction from the gas intake to the gas exit. The coverof the disk assembly covers the open end on the side of the gas intake.

The heater heats up the disks so that NH₄Cl is prevented from attachingto the disks contained in the disk assembly. The heater can bestructured as to surround the circumference of the housing or can bearranged inside the housing.

Gas from the gas intake flows into a gap between the disk assembly andthe housing, passes through gaps between the disks, flows into an innerspace of the disk assembly, and is discharged from the gas exit. Thehydrocarbon C_(x)H_(v), etc., as a reactive product which is producedwhen producing SiO₂ from TEOS, is attached to each disk while theexhaust gas is passing through the gaps between the disks.

The switching trap TRP2 is used for absorbing NH₄Cl from the exhaustgas. The switching trap TRP2 includes a plurality of water-cooled traps,which are arranged in parallel with each other and absorb NH₄Cl from theexhaust gas passing through the disk assembly, a switch and a cleaningroom.

Each of the water-cooled traps included in the switching trap TRP2includes a housing, a cooling device and an in/outflow section. Thehousing of each water-cooled trap has a gas intake through which theexhaust gas flows in and a gas exit through which the exhaust gas flowsout. The cooling device of each water-cooled trap is arranged within thehousing. The in/outflow section of each water-cooled trap is a sectionthrough which cool water circulating through the cooling device flows inand out. The cooling device includes a cool water circulator, whichcools down by applying cool water thereto, and a plurality of coolingfins, which are arranged on the surface of the cool water circulator.

The gas from the gas intake hits the cooling device and contacts thecooling fins, thereby cooling down. By doing this, ammonium chlorideNH₄Cl, to be separated from the exhaust gas as a result of the cooling,as a reactive product produced when a silicon nitride film is producedby a chemical reaction of ammonia and dichlorosilane is deposited on thecooling device. The exhaust gas from which NH₄Cl has been removed isdischarged from the gas exit into the vacuum pump VP.

When the exhaust gas passes through one of the water-cooled trapsincluded in the switching trap TRP2, the switch causes the exhaust gasto pass through another trap in accordance with operations of anoperator. Subsequently, the exhaust gas flowing through the trap throughwhich the exhaust gas has been already flowing is interrupted under thecontrol of the switch which then connects the trap to the cleaning room.Then, water stored in the cleaning room is pressurized by a pumpincluded in the cleaning room and flows into the trap connected to thecleaning room. The water which has flowed thereinto cleans NH₄Clcontained in the trap, flows back to the cleaning room and is dischargedfrom the cleaning room, thereafter fresh water is stored in the cleaningroom.

In repeating the above steps, each of the water-cooled traps of theswitching traps TRP2 is cleaned while the exhaust gas is passing throughany other trap. Therefore, the switching trap TRP2 lets the exhaust gascontinuously flow therethrough, and absorbs NH₄Cl from the exhaust gas.

The combination valve CV includes a valve, a valve controller and apressure detector and is arranged for automatically controlling pressurewithin the reaction tube 11.

The pressure detector detects the pressure within the pipes 63 a and 63b and informs the valve controller of the detected pressure. The valvecontroller adjusts an opening degree of the valve in such a way that thepressure detected by the pressure detector reaches a predeterminedvalue. Furthermore, the valve controller controls an amount of theflowing exhaust gas which flows from the hot disk trap TRP1 into theswitching trap TRP2. Thus, the pressure within the pipes 63 a and 63 bis controlled at an optional (or desired) value by the combination valveCV.

The combination valve CV adjusts and maintains the pressure in the pipes63 a and 63 b at an arbitrary value substantially in a range between 0and 1013 hpa, without using any other valve arranged in parallel to thecombination valve CV.

A mechanism for opening and closing the path through which the exhaustgas flows can be simply structured with using the combination valve CV.Thus, the path does not necessarily have the structure, which includes aplurality of valves or pipes for conducting the exhaust gas in parallelto the plurality of valves, and which is so complicated as to cause theconductance of the path to be lowered. As a result of this, it becomespossible to prevent the path from including a portion where theconductance is low and to restrain an increase in a portion whereproducts to be produced is attached.

The vacuum pump VP includes the intake and the vent, and has adisplacement volume of approximately 15000 to 20000 liter/min.

One end of the pipe 63 c is connected to the vent of the vacuum pump VP.The other end of the pipe 63 c is split into two, one of which is thefirst vent 71 and the other one of which is the second vent 72. Thefirst vent 71 is used for exhausting the exhaust gas when producing asilicon oxide film SiO₂ and a silicon nitride film Si₃N₄. The secondvent 72 is used for exhausting hydrogen fluoride gas used for cleaning.The pipe 63 c includes a valve 69, which switches the first and secondvents 71 and 72 from one to the other, thereby discharging the exhaustgas discharged from the vacuum pump VP.

A first scrubber 73 which scrubs an unreacted substance(SiC_(x)H_(y)O_(z))_(n), ammonium chloride (NH₄Cl), ammonia, etc. isarranged in the first vent 71. A second scrubber 74 which scrubshydrogen fluoride, etc. is arranged in the second vent 72.

All of the heater 16, the mass flow controller 34 a to 34 c, thecombination valve CV, the gas sources 35 a to 35 d, 36 a and 36 b, thevalves VB1 to VB6, the elevator mechanism 54, the vacuum pump VP and theexhaust path heater 65 are connected to a controller 75 which controlsthose all. The controller 75 measures the temperature and the pressureof each part of the vertical heat treatment apparatus using a sensor.Further, the controller 75 automatically controls a series of processes,as will be explained later, by sending a control signal, etc., to eachpart of the apparatus.

An explanation will now be made to exemplary operations of the verticalheat treatment apparatus, wherein a silicon oxide film SiO₂ and asilicon nitride film Si₃N₄ are formed, thereafter the inner part of thevertical heat treatment apparatus is cleaned.

A series of processes, as will be explained below, are carried out andautomatically controlled by the controller 75.

As illustrated in FIG. 2, in a case where the elevator mechanism 54 islowered down, the wafer boat 14 containing the semiconductor substrates(wafers) 15 is placed on the heat insulating cylinder 53 on the lid 51.In this case, the heater 16 is heated in a range approximately between700° C. and 800° C.

In a case where the elevator mechanism 54 is lifted, the lid 51 and thewafer boat 14 are moved upward, thereby loading the wafer boat 14 intothe reaction tube 11. In this case, the vacuum pump VP is operated andthe opening degree of the combination valve CV is controlled, in a statewhere the factory exhaust valve EV is closed. Then, the wafer boat 14 isloaded while the gas inside the reaction tube 11 is absorbed at apressure of approximately −500 Pa with respect to the (atmosphere)pressure inside the reaction tube 11. As exemplarily illustrated in FIG.3, particles in the reaction tube 11 are absorbed, therefore, theparticles are prevented from being attached to the semiconductorsubstrates 15.

Upon completion of loading the wafer boat 14 into the reaction tube 11,the flange 22 formed under the manifold 17 and the lid 51 arehermetically connected with each other via the “O” ring 52. In thiscase, the opening degree of the combination valve CV is controlled andslow exhaustion is performed along the pipes (i.e., at an exhaustionspeed at which the reactive products on the semiconductor substrates 15to be heat-treated and the reactive products inside the reaction tube 11are not messed up). Thereafter, the reaction tube 11 is decompressed ata predetermined pressure value, for example, in a range between 0.5 and0.7 Pa.

If the pressure within the reaction tube 11 reaches a predeterminedvalue, the valves VB1 and VB2 are open. Then, NH₃ and SiH₂Cl₂ aresupplied respectively from the first gas source 35 a and the second gassource 35 b into the reaction tube 11, and the temperature of thesemiconductor substrates 15 is controlled in a range between 600° C. and700° C. The exhaust path heater 65 heats the pipe 63 a and thecombination valve CV to a temperature in a range approximately between100° C. and 150° C. The valve 69 of the pipe 63 c selects a path throughwhich the exhaust gas can be exhausted after being scrubbed through thefirst scrubber 73 from the first vent 71.

Furthermore, the opening degree of the combination valve CV iscontrolled, thereby the exhaust gas is continuously exhausted while thepressure within the reaction tube 11 is controlled in a range between 25Pa and 50 Pa. Such a state where the pressure in the reaction tube 11 isthus controlled is maintained for a predetermined time period, forexample, two hours or so.

Meanwhile, a reaction takes place in the reaction tube 11, and a siliconnitride film (Si₃N₄ film) is formed on the surface of each semiconductorsubstrate 15. The reaction is represented by the following chemicalformula (1).

10NH₃+3SiH₂Cl₂→Si₃N₄+6NH₄Cl+6₂  (1)

While the silicon nitride film is formed thereon, the heater of the hotdisk trap TRP1 heats each disk contained in the hot disk trap TRP1 to atemperature between 100° C. and 150° C. By doing this, it becomespreventable that the exhaust gas cools off by the disks. Moreover, NH₄Clincluded in the exhaust gas is prevented from attaching to the disks.

During the formation of the film, NH₄Cl contained in the exhaust gascools down and is collected in the switching trap TRP2.

The exhaust gas flowing from the switching trap TRP2 is absorbed by thevacuum pump VP, and scrubbed by the scrubber 73 arranged in the firstvent 71 of the pipe 63 c, thereby being exhausted therefrom.

In addition to the above, in the meantime, Si₃N₄ and a very small amountof NH₄Cl as reactive products are attached to the inner wall of thereaction tube 11, the manifold 17, the exhaust pipe 61, the pipe 63, thetraps TRP1 or TRP2 or the combination valve CV.

When the silicon nitride film Si₃N₄ is completely formed, the valves VB1and VB2 are closed, and NH₃ and SiH₂Cl₂ are no longer supplied into thereaction tube 11. Then, while the vacuum pump VP is being driven, theopening degree of the combination valve CV is controlled so that slowexhaustion can be performed along the pipes. Then, the reaction tube 11is decompressed approximately at a pressure value of 0.1 Pa.

When the pressure in the reaction tube 11 reaches a predetermined value,the valve VB5 is open, so that alkoxysilane (preferably TEOS) can besupplied into the reaction tube 11 from the third gas source 35 c. Atthe same time, the temperature of the semiconductor substrates 15 iscontrolled at a temperature of approximately 700° C. by the heater 16.The exhaust path heater 65 retains the temperature of the pipe 63 a andthe combination valve CV in a range between 100° C. and 150° C.Thereafter, the opening degree of the combination valve CV iscontrolled, and the exhaust gas is continuously exhausted while thepressure within the reaction tube 11 is controlled at a pressure valueof 50 Pa. Such a state where the pressure in the reaction tube 11 isthus controlled is maintained for a predetermined time period, forexample, twenty minutes or so.

In a case where TEOS is to be supplied from the third gas source 35 c, areaction occurs in the reaction tube 11, thereby a silicon oxide film(SiO₂ film) is formed on the surface of each semiconductor substrate 15.The reaction is represented by the following chemical formula (2).

 TEOS→SiO₂+C_(x)H_(y)+H₂O  (2)

where x and y are both natural numbers.

Since the exhaust conductance is decreased in the hot disk trap TRP1,hydrocarbon C_(x)H_(y) contained in the exhaust gas is attached to thedisks and removed from the exhaust gas.

The exhaust gas contains NH₄Cl owing to sublimation of NH₄Cl attached toperiphery of the manifold 17 or the exhaust pipe 61, which is at arelatively low temperature, during the time the Si₃N₄ film was formed.However, because the heater of the hot disk trap TRP1 heats up the disksincluded in the hot disk trap TRP1 in a range from 100° C. to 150° C.,NH₄Cl is collected by the switching trap TRP2 without attaching to thedisks.

The exhaust gas flowing from the switching trap TRP2 is scrubbed by thefirst scrubbers 73 and exhausted therefrom, after being supplied fromthe first vent 71, which is selected by the valve 69 of the pipe 63 c,via the vacuum pump VP.

It should be noted that, during the formation of the film, silicon oxideSiO₂ attaches to the inner wall of the reaction tube 11. A certainamount of silicon oxide SiO₂ or hydrocarbon C_(x)H_(y) attaches to sucha section in which the conductance is low or dynamically varies or tothe dead space on the gas-flowing path, as the lower portion of themanifold 17, the exhaust port 61, the bent portion of the pipe 63 a orthe inner section of the hot disk trap TRP1.

After the film is completely formed, the valve VB6 is closed, so thatTEOS is no longer supplied into the reaction tube 11. Then, the reactiontube 11 is decompressed at a pressure value in a range from 0.5 Pa to0.7 Pa by the vacuum pump VP. Subsequently, the combination valve CV isclosed, whereas the valves VB3 and VB4 are open. Now, nitrogen gas issupplied from the nitrogen gas sources 36 a and 36 b into the reactiontube 11, thus, the reaction tube 11 is back into an atmospheric statewhere the pressure within the reaction tube 11 is a normal value.

Afterwards, the reaction tube 11 is left for a predetermined timeperiod, for example, fifteen minutes or so, and cools down.

Next, the combination valve CV is open, and its opening degree iscontrolled. The gas within the reaction tube 11 is absorbed at apressure value of −500 Pa with respect to the pressure (i.e. atmospherepressure) inside the reaction tube 11. At the same time, as shown inFIG. 2, the elevator mechanism 54 is driven, and the wafer boat 14 islowered down and unloaded from the reaction tube 11, so that thesemiconductor substrates 15 are unloaded.

When the wafer boat 14 is unloaded, NH₄Cl attached to a section of thereaction tube 11 whose temperature is low is sublimated when thehigh-temperature semiconductor substrates 15 after heat-treated pass bythe reaction tube 11. The sublimated gas reacts with hydrogen, therebyparticles may be produced. However, in employing such an unloadingmethod, as exemplarily shown in FIG. 3, the sublimated gas or theparticles are gently absorbed and exhausted from the reaction tube 11,without attaching to the semiconductor substrates 15.

The semiconductor substrates 15 are unloaded together with the waferboat 14 and are removed onto a cassette as needed.

In order to clean the inside of the vertical heat treatment apparatus,the elevator mechanism 54 is lifted up, while the lid 51 is movedupward. The flange 22 of the manifold 17 and the lid 51 are hermeticallyconnected with each other through the “O” ring 52. In a case where toclean the wafer boat 14 together with the inside of the apparatus, thewafer boat 14 from which semiconductor substrates 15 have already beenremoved is arranged on the heat insulating cylinder 53.

The valve 69 of the pipe 63 c so selects a path as the exhaust gas to beexhausted from the second vent 72.

In a state where the vacuum pump VP is activated and the combinationvalve CV is controlled, the pipe 63 a is decompressed at a pressurevalue in a range from 10 kPa to 30 kPa. The heater 16 heats up theinside of the reaction tube 11 approximately to a temperature of 50° C.The heater of the hot disk trap TRP1 heats up the disks contained in thehot disk trap TRP1 to a temperature approximately between 100° C. to150° C. The exhaust path heater 65 heats up the pipe 63 c and thecombination valve CV to a temperature approximately between 100° C. to150° C.

Next, the valve VB6 is open, so that hydrogen fluoride is supplied tothe inlets 64 a to 64 c for a predetermined time period, for example,ten minutes or so. The hydrogen fluoride so flows into the lower portionof the manifold 17 from the inlet 64 a as to clean the lower portion andthe inner wall of the inner tube 13, and gradually goes upward to cleanthe upper portion thereof. The fluoride hydrogen drops down to the gapbetween the outer tube 12 and the inner tube 13, cleans the outer wallof the inner tube 13 and the inner wall of the outer tube 12, and flowsinto the exhaust port 61.

The hydrogen fluoride flows onto the upstream side of the bent point ofthe pipe 63 a from the inlet 64 b. Furthermore, the hydrogen fluorideflows into the gas intake of the hot disk trap TRP1 from the inlet 64 cand flows toward the vacuum pump VP.

By the hydrogen fluoride supplied to the inlets 64 a to 64 c, thesilicon nitride Si₃N₄ or the silicon oxide SiO₂ which has attached tothe inner wall of the reaction tube 11, and the hydrocarbon C_(x)H_(y)attached to the lower portion of the manifold 17, the bent portion ofthe pipe 63 a or the inside of the hot disk trap TRP1, are separated(i.e., such portion is cleaned) therefrom and exhausted from the secondvent 72 selected by the valve 69 via the vacuum pump VP. At this time,the hydrogen fluoride is scrubbed by the second scrubber 74.

Upon completion of the cleaning, the valve VB6 is so closed the fluoridehydrogen is no longer supplied. Then, the reaction tube 11 isdecompressed at a pressure value between 0.5 Pa and 0.7 Pa by the vacuumpump VP. Subsequently, in order to perform purging, the valves VB3 andVB4 are open, and nitrogen gas is supplied into the reaction tube 11from the nitrogen gas sources 36 a and 36 b. After repeating this step afew times, the reaction tube 11 is back into an atmospheric state wherethe pressure within the reaction tube 11 is a normal value.

In the vertical heat treatment apparatus according to the firstembodiment of this invention, reactive products produced during theformation of the films can be appropriately removed from the exhaust gasin the heat treatment apparatus which forms a plural types of films.Furthermore, products (main products and reactive sub products) whichhave attached into the apparatus can easily be removed without breakingdown the apparatus. Thus, the apparatus can be utilized with enhancedefficiency, and a decrease in the maintenance cost can be achieved.

At the time of cleaning, mixture gas of hydrogen fluoride and anotherkind of gas may be supplied into the reaction tube 11 and the exhaustpipe 63. For example, during the cleaning, the valves VB6 and VB3 (orVB4) are so open as to conduct hydrogen fluoride and nitrogen into thereaction tube 11 and the exhaust pipe 63.

The temperature of the reaction tube 11, when cleaning the apparatus, isnot limited to 50° C., however, its temperature may set in a rangebetween 30° C. to 200° C. in an appropriate manner and time.

Second Embodiment

In the first embodiment, when hydrogen fluoride is so supplied to theinlets 64 a to 64 c after the formation of the films as to clean theinside of the apparatus, the pressure within the pipe 63 a is retainedat an appropriate pressure value between 10 kPa and 30 kPa.

In general, when the hydrogen fluoride, is so supplied thereto as toclean the apparatus, cleaning the apparatus is advantageously performedwhen the pressure within the pipe is 10 kPa or higher. In a case wherethe pressure within the pipe 63 a is approximately 20 kPa, attachedproducts are most likely to be removed. However, the pressure ismaintained at a given value in a range from 10 kPa to 30 kPa, thehydrogen fluoride hardly reaches a section in which the conductance ofthe gas is low or a section in which no fresh gas flows, thus, theattached products remains without being removed. For example, themanifold 17 as the lower portion of the reaction tube 11 is formed to beuneven, since the gas supplying pipes 31 a to 31 c are insertedthereinto, therefore, the hydrogen fluoride gas is not likely to beinfiltrated into the manifold 17. The hydrogen fluoride gas is notlikely to be infiltrated also into the periphery of the bent portions ofthe exhaust pipe 63 or joint sections of pipes. Thus, the products (mainproducts or reactive sub products) attached to the inner wall of themanifold 17 or the exhaust pipe 63 remain, that is, such products arenot properly and desirably removed.

In the vertical heat treatment apparatus according to the secondembodiment of this invention, at the time of cleaning the apparatus, thepressure within the reaction tube 11 is repeatedly fluctuated. Thiscauses the hydrogen fluoride gas to be infiltrated into the reactiontube 11 and the attached products to be appropriately removed therefrom.

The vertical heat treatment apparatus according to the second embodimenthas the same structure as that of the vertical heat treatment apparatusaccording to the first embodiment.

At the time of cleaning the apparatus, likewise in the first embodiment,the elevator mechanism 54 is lifted up, so that the lid 51 is movedupward. Then, the flange 17 and the lid 51 are hermetically connectedwith each other via the “O” ring 52. In a case where to clean the waferboat 14 as well together with the inside of the apparatus, the waferboat 14 from which the semiconductor substrates 15 have already beenremoved is arranged on the heat insulating cylinder 53.

The valve 69 of the pipe 63 c selects a path such that the exhaust gasis exhausted from a second vent 72.

In a state where the vacuum pump VP is activated and the combinationvalve CV is controlled, the pipe 63 c is decompressed into a pressurevalue of 10 kPa. The heater 16 heats up the inside of the reaction tube11 approximately to a temperature of 50° C., The heater of the hot disktrap TRP1 heats up the disks contained in the hot disk trap TRP1 to atemperature approximately between 100° C. to 150° C. The exhaust pathheater 65 heats up the pipe 63 c and the combination valve CV to atemperature approximately between 100° C. to 150° C.

Next, the valve VB6 is open, and hydrogen fluoride is supplied into theinlets 64 a to 64 c for a predetermined time period, for example, tenminutes or so. The hydrogen fluoride flows into the lower portion of themanifold 17 from the inlet 64 a, flows into the upstream side of thebent portion of the pipe 63 a from the inlet 64 b, flows into the gasintake of the hot disk trap TRP1 from the inlet 64 c, and flows towardthe vacuum pump VP.

By the hydrogen fluoride supplied to the inlets 64 a to 64 c, thesilicon nitride Si₃N₄ and the silicon oxide SiO₂ which attaches to theinner wall of the reaction tube 11, or the hydrocarbon C_(x)H_(y)attached to the lower portion of the manifold 17, bent portion of thepipe 63 a or the inside of the hot disk trap TRP1, is separated (i.e.,such portion is cleaned) therefrom, and exhausted from the second vent72 selected by the valve 69 via the vacuum pump VP.

In this case, the combination valve CV is controlled, and the pressurewithin the pipe 63 a is fluctuated in a range from 0.1 kPa to 30 kPa.for example.

In other words, the opening degree of the combination valve CV is sethigh, and the vacuum pump VP causes the pipe 63 c to be decompressed.After the pipe 63 a is decompressed approximately at a pressure value of0.1 kPa, the opening degree of the combination valve CV is set low, andthe pressure within the pipe 63 a raises at a pressure value between 20kPa to 30 kPa.

The range in which the pressure within the pipe 63 a is fluctuated isdetermined by the exhausting performance of the vacuum pump VP. It ispreferred that the hydrogen fluoride is infiltrated into the reactiontube 11 or a section of the exhaustion pipe 63 in which the conductanceis low. To be specific, the minimum range in which the pressure isfluctuated is not limited to the pressure value of 0.1 kPa. Instead, theminimum range can be set at a pressure value of 2 kPa (1 to 3 kPa), forexample, as long as the fluoride hydrogen can be infiltrated and can beremoved at that pressure value.

FIG. 4 is a diagram exemplifying a pressure fluctuation of the pipe 63a, when the pressure within the reaction tube 11 is repeatedlyfluctuated so as to clean the pipe 11.

In the exemplary illustration, the pressure within the pipe 63 a isfluctuated in a range approximately between 2 kPa to 30 kPa.Particularly, the pressure within the pipe 63 a is fluctuated in such away that a period in which the pressure is 10 kPa or higher and a periodin which the pressure is lower than 10 kPa are cyclically repeated.

At that time, as explained above, cleaning the apparatus isadvantageously performed by supplying the hydrogen fluoride gas when thepressure within the pipe is 10 kPa or higher. It is, therefore,preferred that the combination valve CV and the vacuum pump VP are socontrolled that the period in which the pressure within the pipe 63 a is10 kPa or higher can be obtained as long as possible.

If the pressure within the reaction tube 11 is thus fluctuated, thefluoride hydrogen gas is filtrated into a section of the reaction tube11 or the exhaust pipe 63 in which the conductance is low. Thus, theattached products can effectively be removed.

Third Embodiment

The method for removing the hydrogen fluoride gas used for cleaning theapparatus, as described in the first and second embodiments, can also beachieved by alternately repeating supplying and vacuuming nitrogen(purge) gas.

For example, as illustrated in the sequence diagram shown in FIG. 5,after cleaning the apparatus with the hydrogen fluoride gas andvacuuming the gas, the cycle of supplying and vacuuming the nitrogen gasis repeated for eleven times (eleven cycles). Then, the hydrogenfluoride gas which remains within the reaction tube 11 and the exhaustpipe 63 can be removed.

The hydrogen fluoride stays in a section, in which the conductance islow, and attaches into the reaction tube 11 and the exhaust pipe 63. Itshould be noted, therefore, that the hydrogen fluoride gas can notefficiently be removed merely by alternately repeating the cycles ofsupplying and vacuuming the nitrogen gas. Despite that performing theprocess shown in FIG. 5 takes approximately five hours (i.e., it isquite time consuming), the fluoride hydrogen of 10 ppm or more remainswithin the reaction tube 11 and the exhaust pipe 63.

In the vertical heat treatment apparatus according to the thirdembodiment of this invention, the hydrogen fluoride which remains withinthe reaction tube 11 after cleaning the pipe can be removed in a shorttime using alkoxysilane (preferably TEOS).

The vertical heat treatment apparatus according to the third embodimentto this invention has the same structure as that of the vertical heattreatment apparatus of the first and second embodiments.

FIG. 6 is a sequence diagram showing operations of the vertical heattreatment apparatus for removing the used hydrogen fluoride gas.

An explanation will now be made to the operations of the vertical heattreatment apparatus which are described in the sequence diagram shown inFIG. 6.

In the vertical heat treatment apparatus, after cleaning the inside ofthe reaction tube 11 and the exhaust pipe 63 using the hydrogen fluoridethe valve VB6 is so closed that the hydrogen fluoride is no longersupplied. Then, the vacuum pump VP is activated, and the reaction tube11 is decompressed.

Next, while the vacuum pump VP is still activated, the valves VB3 andVB4 are open in order to supply nitrogen gas into the reaction tube 11from the nitrogen gas sources 36 a and 36 b. Then, the opening degree ofthe combination valve CV is controlled, thereby the reaction tube 11 isset back at a pressure value of approximately 30 kPa. The heater 16heats up the inside of the reaction tube 11 approximately to atemperature of 650° C.

Now, the valves VB3 and VB4 are so closed that the nitrogen gas is nolonger supplied into the reaction tube 11. The reaction tube 11 is againdecompressed by the vacuum pump VP.

Decompressing the reaction tube 11 and supplying the nitrogen gasthereinto are repeatedly performed for a given number of times, forexample, three times (three cycles).

After having thus repeated decompressing the reaction tube 11 andsupplying the nitrogen gas thereinto, in a case where the reaction tube11 is decompressed, the valve VB5 is open so as to supply alkoxysilane(preferably TEOS) into the reaction tube 11 from the third gas source 35c. In a state where the pressure within the reaction tube 11 iscontrolled approximately at 133 Pa after the opening degree of thecombination valve CV is controlled, exhaustion of the gas iscontinuously performed for a predetermined time period, for example, twominutes or so.

Next, the valve VB5 is closed so that alkoxysilane gas (reactant gas) isno longer supplied, whereas the valves VB3 and VB4 are open so as tosupply nitrogen gas into the reaction tube 11 from the nitrogen gassources 36 a and 36 b. The opening degree of the combination valve CV iscontrolled so that the pressure within reaction tube 11 is set back at apressure value of approximately 30 kPa. Then, the reaction tube 11 isleft for a given time period, for example, fifteen minutes or so,thereby cooling down.

Next, after controlling all of the vacuum pump VP, the valves VB3 andVB4 and the combination valve CV, decompressing the reaction tube 11 andsupplying the nitrogen gas thereinto are repeatedly performed for agiven number of times, for example, three times (three cycles).

By doing this, the hydrogen fluoride which remains within the reactiontube 11 can completely be removed approximately within four hours. Inother words, a reduction in the time necessary for removing the reactiveproducts attached to the inside of the pipe can be achieved.

Before or after supplying TEOS into the reaction tube 11, the number ofcycles taken to supply the nitrogen gas and to vacuum the gas is notlimited to three, and the time required for the three cycles is notlimited 72 minutes. Instead, as long as the hydrogen fluoride can beremoved, the number of cycles and the continuous time period canarbitrarily be set.

The gas to be supplied for removing the hydrogen fluoride is not limitedto alkoxysilane for forming a silicon oxide film, instead, NH₃ andSiH₂Cl₂ for forming a silicon nitride film can be employed. Gas forforming a film to be formed in the reaction tube 11 can be supplied forremoving the hydrogen fluoride.

The present Invention is not limited to the above-described first tothird embodiment, however various embodiments and changes can be made.

For example, in the above-described embodiments, the combination valveCV is employed for opening and closing a gas-flowing path in a rangefrom the reaction tube 11 to the vacuum pump VP. However, a main valve,a sub valve which opens and closes its own path and a by-pass pipe whichis arranged across the main valve may be employed in place of thecombination valve CV. In such a structure, the gas is slowly exhaustedin the above-described film forming process, or the gas is exhaustedwhen the semiconductor substrates 15 are unloaded. Specifically, theopening degree of the sub valve is adjusted while the main valve isclosed, so that the gas can be slowly exhausted or can simply beexhausted even when the semiconductor substrates 15 are unloaded.

The position or section into which the hydrogen fluoride for cleaningthe apparatus is conducted can be arbitrarily determined. Inlets arearranged in arbitrary portions, to which products are very likely toattach. Such products are produced while forming the film, because thetemperature of the exhaust gas is decreased or the conductance of theexhaust gas is lowered. The hydrogen fluoride stored in the fourth gassource 35 d can be conducted into a gas-flowing path through the inlets.

For example, as illustrated in FIG. 7, in place of the inlet 64 a, aninlet 64 d may be arranged in a position adjacent to the joint 62, sothat only the inside of the exhaust port 61 and the exhaust pipe 63 canbe cleaned.

An explanation will now exemplarily be made to the structure of theinlet 64 d with reference to FIGS. 8A and 8B. In the examples shown inFIGS. 8A and 8B, an HF introduction pipe 81 included in the inlet 64 dis arranged in such a way that it is inserted through a hole formed inthe side wall of the exhaust pipe 63 a (or the exhaust port 61), andthat it stays by an intake 61 a of the exhaust port 61 along the innersurface of the exhaust pipe 63 a and the exhaust port 61. One end of theHF introduction pipe 81 is bent perpendicularly to the center of theexhaust port 61 in a position adjacent to the opening 61 a of theexhaust port 61.

According to this structure, an opening 81 a of the HF introduction pipe81 faces the inner surface of the exhaust port 61. Thus, as shown witharrows AR in FIG. 8B, HF gas supplied from the fourth gas source 35 dspouts out from the opening 81 a toward the inner surface of the exhaustport 61, and so hits the inner wall as to spread into two, the upstreamand down stream sides. As the entire gas flows onto the downstream sideby the vacuum pump VP, the spouted HF gas entirely flows onto thedownstream side and is supplied into the entire inner wall of theexhaust port 61 and the exhaust pipe 63, resulting in the reactiveproducts being evenly removed. There is a sudden decrease in exhaustconductance of the connected portion of the reaction tube 11 and theexhaust port 61. Therefore, reactive products are very likely to attachinto the inner surface of the exhaust port 61. When the inlet 64 d isstructured as shown in FIGS. 8A and 8B, the reactive products which haveattached to the inner surface of the exhaust port 61 can be removedtherefrom with efficiency. The HF gas does not directly hit the innerwall of the inner tube 13, thereby preventing the side wall of the innertube 13 from being etched.

It is also possible that the inlet 64 d have any one of the structuresshown in FIGS. 9 to 12.

In the structure shown in FIG. 9, the HF introduction pipe 81 isarranged in such a way that it is inserted from a pipe wall of theexhaust pipe 63 a, and that its one end is bent in a position which isslightly on the upstream side relative to the intake 61 a of the exhaustport 61. The opening 81 a of the HF introduction pipe 81 faces thedownstream in a position facing the intake 61 a of the exhaust port 61.

In the structure shown in FIG. 10, the HF introduction pipe 81 isinserted from the side wall of the manifold 17. The opening 81 a of theHF introduction pipe 81 arranged along the inner wall of the manifoldfaces the intake 61 a of the exhaust port 61.

In the structure shown in FIG. 11, two holes 83 and 85 for dischargingHF gas are formed right in a part where the HF introduction pipe 81 isperpendicularly bent. In such a structure, HF gas can be supplied alongthe inner surface of the exhaust port 61, therefore, reactive productswhich have attached to the inner wall of the exhaust port 61 can beremoved with efficiency. The inlet 64 d may be structured such that theopening 81 a is so closed as HF gas to spout out from the two holes 83and 85.

In the structure shown in FIG. 12, the end of the HF introduction pipe81 is split into two, so that HF gas can be supplied from the two splitends in the two opposite direction, thereby promoting efficiency withwhich reactive products are removed therefrom.

The structure shown in FIGS. 8A and 8B, 9 or 10 and the structure shownin FIG. 11 or 12 are possibly combined, For example, the HF introductionpipe 81 is formed with the structure, shown in FIGS. 8A and 8B, or FIG.9 or 11, in which two holes are arranged in its end. In doing this, HFgas can be supplied axially along the exhaust port 61 or in a pluralityof directions along the inner surface.

The number of inlet(s) and the position where the inlet is arranged arenot limited to those described in the structure shown in FIG. 1 or 7.For example, there can be arranged only one inlet 64, along whichhydrogen fluoride is inserted into the reaction tube 11, thereaftercleaning the exhaust pipe 63 with the hydrogen fluoride flowing from thereaction tube 11.

In the third embodiment, film-forming gas to be supplied when exhaustinghydrogen fluoride may be supplied into the reaction tube 11 and/or theexhaust pipe 63 from a pipe which is not the one for supplyingfilm-forming gas when forming films.

A single water-cooled trap which is substantially the same as thatincluded in the switching trap TRP2 may be arranged in place of theswitching trap TRP2, for example.

The pipe which serves as a joint connecting the hot disk trap TRP1 tothe combination valve CV and the pipe which serves as a joint connectingthe combination valve CV to the switching trap TRP2 may be heated to atemperature in a range between 100° C. to 150° C., during the sameperiod of time as the exhaust path heater 65 performs heating. Thus,hydrocarbon C_(x)H_(y) or NH₄Cl are not likely to attach into suchpipes.

In the above-described embodiments, while the gas is exhausted by meansof the vacuum pump VP, the semiconductor substrates 15 are loaded orunloaded into the reaction tube 11. However, the method for exhaustingthe gas within the reaction tube 11 is arbitrary. For example, whenloading/unloading the wafer boat 14, the combination valve CV is closed,whereas the factory exhaust valve EV is open. In this cases, the gaswithin the reaction tube 11 may be controlled by a damper so that thegas pressure thereof is −50 to −700 Pa with respect to the atmospherepressure.

In the above-described embodiments, explanations have been made to anexample, in which a silicon nitride film is formed by a reaction ofammonia and a silicon compound and a silicon oxide film is formed byresolving alkoxysilane. However, source gas is arbitrary, and any othersource gas can be used.

This invention is not limited to the case where a silicon nitride filmand the silicon oxide film are formed, instead, is applicable to anyother various film-forming processes. For example, this invention can beused when forming a TiN film on a substrate to be heat-treated by areaction of TiCl₄ gas and NH₃ gas (NH₄Cl is produced as a reactive subproduct), and when using an organic silicon compound as source gas otherthan alkoxysilane, and further when forming a thin film other than amulti-layered insulating film.

In the above-described embodiments, an explanation has exemplarily beenmade to the heat treatment apparatus for forming a film on thesemiconductor substrate (semiconductor wafer). However, this inventionis applicable to an apparatus for forming a film on an arbitrary objectto be heat-treated, such as a glass substrate, etc.

In the above-described embodiments, an explanation has been made to anexample in which nitrogen gas is supplied from the nitrogen gas sources36 a and 36, however, the method of supplying the nitrogen gas is notlimited to the above. For example, as shown in FIG. 13, the gas pipe 33d may be connected to the nitrogen gas source 36 c through the valveVB7, so that the opening degree of the valve VB7 is controlled by thecontroller, thereby supplying the nitrogen gas therethrough.

Various embodiments and changes may be made thereonto without departingfrom the broad spirit and scope of the invention. The above-describedembodiment is intended to illustrate the present invention, not to limitthe scope of the present invention. The scope of the present inventionis shown by the attached claims rather than the embodiment. Variousmodifications made within the meaning of an equivalent of the claims ofthe invention and within the claims are to be regarded to be in thescope of the present invention.

This application is based on Japanese Patent Application No. H10-337879filed on Nov. 27, 1998 and including specification, claims, drawings andsummary. The disclosure of the above Japanese Patent Application isincorporated herein by reference in its entirety.

What is claimed is:
 1. A heat treatment apparatus comprising: a reactiontube which can contain an object to be heat-treated; an exhaust pipe,one end of which is connected to said reaction tube, for exhausting gascontained in said reaction tube; a reactant-gas supplying pipe, which isconducted into said reaction tube, for supplying reactant gas into saidreaction tube; an HF-gas supplying section which includes an HF pipeconnected to a gas source for hydrogen fluoride, an HF valve whichcontrols to supply hydrogen fluoride from the gas source and which isarranged in the HF pipe, and a first inlet for conducting, into saidreaction tube, the hydrogen fluoride supplied from the gas sourcethrough the HF pipe, and a second inlet for conducting, into saidexhaust pipe, the hydrogen fluoride supplied from the gas source throughthe HF pipe, a plurality of traps which are arranged on said exhaustpipe and which remove a reactive product within said exhaust pipe; and apressure control valve disposed between said plurality of traps, thepressure control valve being structured to open and to close agas-flowing path of said exhaust pipe and to control pressure in saidreaction tube and said exhaust pipe at a desired value, wherein the BFvalve is open and the hydrogen fluoride gas is conducted from the gassource into said exhaust pipe and said reaction tube, thereby cleaninginside of said exhaust pipe and said reaction tube, and wherein saidpressure control valve controls the pressure in said exhaust pipe andsaid exhaust pipe to the desired value.
 2. The heat treatment apparatusaccording to claim 1, wherein: other end of said exhaust pipe is splitinto a first and second vents; and a valve is arranged between the firstand second vents, conducts exhaust gas into the second vent when HF gasis exhausted, and conducts exhaust gas into the first vent when no HFgas is exhausted.
 3. The heat treatment apparatus according to claim 1,further comprising: a plurality of traps which are arranged on saidexhaust pipe and which remove a reactive product within said exhaustpipe; and a pressure control valve which is arranged between saidplurality of traps and which maintain pressure within said reaction tubeand said exhaust pipe at an optional value.
 4. The heat treatmentapparatus according to claim 3, wherein said pressure control valvemaintains pressure in said exhaust pipe at a pressure value of 10 kPa orgreater.
 5. The heat treatment apparatus according to claim 1, wherein:said reaction tube includes an inner tube, whose upper end is open, andan outer tube, which surrounds the inner tube with a space and whoseupper ends is closed; and said first inlet conducts HF gas into theinner tube, and said exhaust pipe is connected to the outer tube andexhausts gas from the gap between the inner and outer tubes.
 6. The heattreatment apparatus according to claim 1, wherein: said exhaust pipeincludes at least one bent part; and said inlet is arranged on anupstream side of a gas-flowing path and adjacent to the bent part ofsaid exhaust pipe.
 7. The heat treatment apparatus according to claim 1,wherein said second inlet is arranged on an upstream side of thegas-flowing path relative to said reaction tube and adjacent to the trapof said exhaust pipe.
 8. The heat treatment apparatus according to claim1, wherein: the reactant-gas supplying pipe conducts alkoxysilane intosaid reaction tube in order to form a silicon oxide film on the object,and conducts ammonia and a silicon compound into said reaction tube inorder to form a silicon nitride film on the object; and said reactiontube forms a silicon oxide film on the object by resolving alkoxysilane,and forms a silicon nitride film on the object by a reaction of ammoniaand a silicon compound.
 9. The heat treatment apparatus according toclaim 8, wherein said exhaust pipe includes: an SiO₂ product trap, inthe exhaust pipe, which removes a reactive product produced by resolvingalkoxysilane within said exhaust pipe; an SiN product trap which removesa reactive product produced by a reaction of ammonia and a siliconcompound within said exhaust pipe; and a heater which heats up said SiO₂product trap in a range between 100 to 150° C.
 10. The heat treatmentapparatus according to claim 9, comprising the pressure control valvefor maintaining pressure within said exhaust pipe at an optional valueand the heater heating the pressure control valve between said SiO₂product trap and said SiN product trap, by controlling an opening degreeof a gas-flowing path of said exhaust pipe.
 11. The heat treatmentapparatus according to claim 8, wherein said exhaust pipe includes: anSiO₂ product trap, arranged in the exhaust pipe, which includes a disktrap and removes a reactive product produced by resolving alkoxysilanewithin said exhaust gas; an SiN product trap, arranged in downstreamside of the gas-flow path of the exhaust pipe from the SiO₂ producttrap, which includes a switching trap and removes a reactive productproduced by a reaction of ammonia and a silicon compound in said exhaustgas; and a heater which heats up said SiO₂ product trap in a rangebetween 100 to 150° C.
 12. The heat treatment apparatus according toclaim 11, a heater that heats the pressure control valve.
 13. The heattreatment apparatus according to claim 1, further comprising a heaterwhich heats up said exhaust pipe to a temperature in a range from 100 to150° C.
 14. The heat treatment apparatus according to claim 1, furthercomprising a pressure controller which controls pressure of hydrogenfluoride within said exhaust pipe to be fluctuated.
 15. The heattreatment apparatus according to claim 14, wherein said pressurecontroller controls the pressure within said exhaust pipe to befluctuated in a range between 0.1 kPa to 30 kPa.
 16. The heat treatmentapparatus according to claim 14, wherein said pressure controllercontrols the pressure within said exhaust pipe to be fluctuated in sucha way that a period at which the pressure is 10 kPa or higher and aperiod at which the pressure is lower than 10 kPa are cyclicallyrepeated, and that the period at which the pressure is 10 kPa or highercan be obtained longer than the period at which the pressure is lessthan 10 kPa.
 17. The heat treatment apparatus according to claim 14,wherein said pressure controller controls the pressure within saidexhaust pipe to be fluctuated in a range between 0.1 kPa to 30 kPa whilethe HF gas is supplied to the reaction tube and the exhaust pipe by saidHF-gas supplying section.
 18. The heat treatment apparatus according toclaim 1, further comprising: a purge-gas supplying section whichsupplies purge gas into said exhaust pipe and said reaction tube; and anexhaust device which is connected to said exhaust pipe, wherein, aftersaid HF-gas supplying section stops supplying hydrogen fluoride, saidpurge-gas supplying section and said exhaust device repeat a pluralityof cycles of exhausting and supplying purge gas into said exhaust pipeand said reaction tube are repeated, and said reactant-gas supplyingpipe supplies reactant gas during the plurality of cycles.
 19. The heattreatment apparatus according to claim 18, wherein: said reactant-gassupplying pipe supplies alkoxysilane as the film-forming gas; and saidpurge-gas supplying section supplies nitrogen gas as purge gas.
 20. Theheat treatment apparatus according to claim 1, further comprising: avacuum pump at downstream side of the gas-flowing path of the exhaustpipe relative to said reaction tube, wherein other end of said exhaustpipe is split into a first and second vents at downstream side of agas-flowing path relative to said reaction tube, wherein a valve isarranged between the first and second vents, conducts exhaust gas intothe second vent when HF gas is exhausted, and conducts exhaust gas intothe first vent when no HF gas is exhausted, and wherein a scrubber forscrubbing the HF gas is disposed in the second vent.
 21. The heattreatment apparatus according to claim 1, further comprising: aplurality of traps which are arranged on said exhaust pipe and whichremove a reactive product within said exhaust pipe, wherein saidpressure control valve measures the pressure in the reaction tube andthe exhaust pipe and controls opening degree of the gas-flowing path ofthe exhaust pipe to control measured pressure at the desired value. 22.The heat treatment apparatus according to claim 1, wherein said pressurecontrol valve maintains pressure in said exhaust pipe at a pressurevalue of 10 kPa or greater while the HF gas is supplied to the reactiontube and the exhaust pipe by said HF-gas supplying section.
 23. The heattreatment apparatus according to claim 1, further comprising a heaterwhich heats up said exhaust pipe to a temperature in a range from 100 to150° C. while the HF gas is supplied to the reaction tube and theexhaust pipe by said HF-gas supplying section.
 24. The heat treatmentapparatus according to claim 1, wherein said second inlet is arranged onan upstream side of a gas-flowing path and adjacent to an entrance ofsaid exhaust pipe.
 25. The heat treatment apparatus according to claim1, further comprising: a cap; a load/unload mechanism; and a controller,wherein said reaction tube includes an opening at one end, wherein saidcap supports the object to be processed and closes the opening of thereaction tube, wherein said load/unload mechanism moves the capsupporting the object, and wherein said controller controls the vacuumpomp and said load/unload mechanism so that the load/unload mechanismmoves the cap to load the object into the reaction tube while exhaustingthe gas in the reaction tube and the exhaust pipe.
 26. The heattreatment apparatus according to claim 25, wherein said controllerexhausts the gas at the 5 to 70 mmH₂O while loading the object into thereaction tube.
 27. The heat treatment apparatus according to claim 1,further comprising: a cap; a load/unload mechanism; and a controller,wherein said reaction tube includes an opening at one end, wherein saidcap supports the object to be processed and closes the opening of thereaction tube, wherein said load/unload mechanism moves the cap, andwherein said controller controls the vacuum pomp and said load/unloadmechanism so that the load/unload mechanism moves down the cap to unloadthe object from the reaction tube while exhausting the gas in thereaction tube and the exhaust pipe.
 28. The heat treatment apparatusaccording to claim 27, wherein said controller exhausts the gas at the 5to 70 mmH₂O while unloading the object from the reaction tube.
 29. Aheat treatment apparatus comprising: a reaction tube which can containan object to be heat-treated; an exhaust pipe, one end of which isconnected to said reaction tube, for exhausting gas contained in saidreaction tube; a reactant-gas supplying pipe, which is conducted intosaid reaction tube, for supplying reactant gas into said reaction tube;at least one trap which are arranged on said exhaust pipe and whichremove a reactive product within said exhaust pipe; a HF-gas supplyingsection which includes: an HF pipe connected to a gas source forhydrogen fluoride, an HF valve which controls to supply hydrogenfluoride from the gas source and which is arranged in the HF pipe, afirst inlet for conducting, into said reaction tube, the hydrogenfluoride supplied from the gas source through the HF pipe, a secondinlet for conducting, into said exhaust pipe, the hydrogen fluoridesupplied from the gas source through the HF pipe, and a third inletwhich is arranged on an upstream side of a gas-flowing path and adjacentto the trap and conducts, into said exhaust pipe, the hydrogen fluoridesupplied from the gas source through the HF pipe; wherein said exhaustpipe includes at least one bent part, and wherein said second inlet isarranged on an upstream side of a gas-flowing path and adjacent to thebent part of said exhaust part.
 30. The heat treatment apparatusaccording to claim 29, further comprising: a fourth inlet which isarranged adjacent to an entrance of said exhaust pipe.
 31. A heattreatment apparatus comprising: a reaction tube which can contain anobject to be heat-treated; an exhaust pipe, one end of which isconnected to said reaction tube; for exhausting gas contained in saidreaction tube; reactant-gas supplying pipes, which is conducted intosaid reaction tube, conducts alkoxysilane into said reaction tube inorder to form a silicon oxide film on the object, and conducts ammoniaand a silicon compound into said reaction tube in order to form asilicon nitride film on the object, said reaction tube forming a siliconoxide film on the object by resolving alkoxysilane, and forming asilicon nitride film on the object by a reaction of ammonia and asilicon compound; an HF-gas supplying section which includes an HF pipeconnected to a gas source for hydrogen fluoride, an HF valve whichcontrols to supply hydrogen fluoride from the gas source and which isarranged in the HF pipe, a first inlet for conducting, into saidreaction tube, the hydrogen fluoride supplied from the gas sourcethrough the HF pipe, and a second inlet for conducting, into saidexhaust pipe, the hydrogen fluoride supplied from the gas source throughthe HF pipe, a plurality of traps which are arranged on said exhaustpipe and which remove a reactive product within said exhaust pipe; and apressure control valve which is arranged between said plurality of trapsand which opens and close the exhaust pipe and maintains pressure withinsaid reaction tube and said exhaust pipe at an optional value, whereinthe HF valve is open and the hydrogen fluoride gas is conducted from thegas source into said exhaust pipe and said reaction tube, therebycleaning both substances formed during forming the silicon oxide filmand silicon nitride film.